Seasonal drink from spa (6,5)

I believe the answer is:

spring water

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'spa' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

'seasonal drink' is the wordplay.
'seasonal' becomes 'spring' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'drink' becomes 'water' (water is an example).
'spring'+'water'='SPRING-WATER'

'from' acts as a link.

Can you help me to learn more?

I've seen this clue in The Mirror.

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